The sound board of an acoustic guitar plays an important role in the sound being produced by the guitar by turning the vibration from the forces exerted by the strings into waves of pressure. The sound board is braced to help distribute the force exerted by the neck of the guitar on the body, and to maintain the tonal responsiveness and structural integrity of the guitar. Bracing also helps controls the manner in which the sound board vibrates as well as stiffens the sound board to minimize distortion of the sound board from the tension applied by the strings. The neck, back, length, box size, and string type also affect the volume and tone, but the actual bracing usually has the greatest impact to the overall sound.
Conventionally there have been many types of bracing systems used with classical acoustic guitars. For instance, ladder bracing involves bracing struts extending from edge to edge of the body perpendicular to the grain of the sound board. Fan bracing is when the struts extend radially outwardly generally below a sound hole, but starting above the bridge location. A problem with these conventional methods is that they become loose either from the adhesive weakening or the guitar getting knocked around from everyday use. Also, as the bracing ages it may lose some of its structural integrity whereby the guitar may become warped and unplayable.
To also counteract the tension created by the strings, a truss rod may be used. A guitar neck is typically made of wood, thus many guitars need a slight truss rod adjustment from either normal wear of the guitar neck from humidity or when switching to a thicker gauged string set. A truss rod is designed to keep the neck straight by countering the pull of the strings and natural tendencies in the wood. A truss rod is typically an interior metal bar that runs the entire length of a guitar's neck.
Loosening a truss rod lowers the amount of resistance counteracting the tension created by the strings causing relief in a guitar neck, also known as forward-bow where there is a slight curvature in the guitar neck bringing the center of the fretboard away from the strings. Intense relief in the guitar neck may cause high action, uncomfortable playing, and may affect the intonation of the guitar. Tightening the truss rod forces the neck to flatten out and bring the center of the fretboard back closer to the strings.
Tightening a truss rod causes the neck to form into a convex shape known as “back-bow” bringing the center of the fretboard closer to the strings. Back-bow may cause the guitar to be played improperly and can cause string buzzing when strung or lead to dead strings. Loosening the truss rod allows the neck to return in alignment and assume a more natural shape under the tension from the strings. Constantly adjusting the truss rod can be quite taxing. When repairing a truss rod, removing the truss rods requires removal of the fingerboard, which in turn requires a complete refret and finish work, proving to be quite expensive.
There have been other attempts to create an acoustic guitar with enhanced structural capability. For example, acoustic guitar models have been made with solid aluminum necks. However these types of guitars failed because the frets were formed into the neck as one solid piece of aluminum. This caused the frets to wear out too quickly because the aluminum was too soft.
There are also guitar designs that incorporate metal rods into the infrastructure to reinforce the bridge underneath the sound board. However the rods are not adjustable and do not incorporate the neck of the guitar, thus not preventing the neck from bowing and warping. Though the guitar industry does have many purists who are looking for a conventional experience, there are many new materials and technologies that may be used to solve these problems. Thus exists a need for a guitar frame that not only provides bracing but also eliminates the need for a truss rod to prevent warping and neck bowing.